1. The problem is to express 0.0025 as a common fraction. 2. Recall that a decimal can be converted to a fraction by writing it over a power of 10. Since 0.0025 has four decimal places, we write it as \frac{25}{10000}. 3. Now simplify the fraction by finding the greatest common divisor (GCD) of 25 and 10000, which is 25. 4. Simplify by dividing numerator and denominator by 25: $$\frac{\cancel{25}}{\cancel{10000}} = \frac{1}{400}$$ 5. Therefore, the common fraction form of 0.0025 is $\frac{1}{400}$.